1. Field of the Invention
The present invention relates to a method for isolating active regions of a substrate through the formation of field oxide regions by local oxidation of silicon (LOCOS), and, more particularly, to a LOCOS process for high density semiconductor devices.
2. Description of the Related Art
The fabrication of semiconductor devices in a substrate requires electrical isolation of the regions of the substrate in which various individual circuit components are formed. The many isolation processes which have been proposed fall into two general groups, processes for forming field oxide (FOX) regions and processes for forming trench isolation regions. In general, processes for forming field oxide regions suffer from the creation of bird's beaks and processes for forming trench isolation regions suffer from the creation of stress induced defects in the substrate.
Bird's beaks, which are caused by lateral growth of oxide during the field oxidation process, serve as stress relief transition regions and help to prevent damage to the substrate caused by physical stresses. However, bird's beaks occupy a significant amount of circuit space, and make it difficult to reduce the size of the active regions defined by the field oxide. Stress may induce defects such as dislocation defects or stacking faults.
Several conventional isolation methods are discussed below.